You can also use sed to remove the | not just referencing the symbol itself but using positional references as in:

$ echo "|abcdefg|" | sed 's:^.\(.*\).$:\1:'
abcdefg

Where ':' are the delimiters (you can replace them with / or any character not in the query, any sign following the s will do it) Here ^ (caret) means at the beginning of the input string and $ (dollar) means at the end. The . (point) that it's after the caret and the one that it's before the dollar sign represents a single character. So in other words we are deleting the first and last characters.
Take in mind this will delete any characters even if | it's not present in the string.